UART - Choosing lsb or msb first

Hi Jack,

Refer this post from Sal : e2e.ti.com/.../1582796
Let me know if this helps you answer your question.

Regards,
Gautam

Jack,

The SCI on the F28335 always transmits LSB first, MSB last (see SPRUFZ5A, p.15, Figure 1-3).  If you need it sent MSB first, you would have to reverse the bit order prior to writing the word to the TXBUF.  There is actually instruction support in the C28x CPU at the assembly code level - the FLIP instruction.  You could write a fairly efficient little function that you pass the TX word to.  It flips the bits, and then writes it to the SCI TXBUF.

Regards,

David

Ok, I managed to flip the bits correctly before adding the data into the TX buffer. Works very good. But I still have problems when receiving data. When I try to read the received data (10 bytes long, added in a 10 bytes array), I can only read one byte. And this byte is wrong ( I have to flip the bits in this byte to get the correct byte).

Maybe since the Msb is received first, and then the lsb, the start bit and the stop bit is flipped aswell? Which means that the data sent looks like : stop bit / data bits / start bit. Is that possible?

I have pasted my code below. I am new to serial communication in c, so I am not sure if I am handling everything correctly (I should maybe check and clear some error and overflow flags etc..).

When I send data to the Peripheral Explorer, i.e. 10 bytes long,, the buffer array gets updated with a same byte for all indexes.

void SCIA_init()
{    
   SciaRegs.SCICCR.all =0x0007;   	// 1 stop bit,  No loopback 27
                                   	// ODD parity,8 char bits,
                                   	// async mode, idle-line protocol
   SciaRegs.SCICTL1.all =0x0003;  	// enable TX, RX, internal SCICLK, 
                                  	// Disable RX ERR, SLEEP, TXWAKE
	
   SciaRegs.SCIHBAUD    = 487 >> 8;	// Highbyte
   SciaRegs.SCILBAUD    = 487 & 0x00FF;	// Lowbyte

   SciaRegs.SCICTL2.bit.TXINTENA = 1; 	// enable SCI-A Tx-ISR
   SciaRegs.SCICTL2.bit.RXBKINTENA = 1; // enable SCI_A Rx-ISR


   ScibRegs.SCIFFTX.all = 0xC028;
   ScibRegs.SCIFFRX.all = 0x0028;
 
   SciaRegs.SCIFFCT.all = 0x0000;	// Set FIFO transfer delay to 0
	
   SciaRegs.SCIFFRX.all = 0xE065;	// Rx interrupt level = 8

   SciaRegs.SCICTL1.all = 0x0023;	// Relinquish SCI from Reset 
} 


interrupt void SCIA_RX_isr(void)
{
	int i;
	char buffer[16];
	for (i=0;i<16;i++) buffer[i]= SciaRegs.SCIRXBUF.bit.RXDT;;

	//if (strncmp(buffer, "Texas", 5) == 0)
	//{
	//	SciaRegs.SCIFFTX.bit.TXFIFOXRESET =1;  // enable TXFIFO
	//	SciaRegs.SCIFFTX.bit.TXFFINTCLR = 1 ;  // force TX-ISR
	//}
	 	
	SciaRegs.SCIFFRX.bit.RXFIFORESET = 0;	// reset RX-FIFO pointer
	SciaRegs.SCIFFRX.bit.RXFIFORESET = 1;	// enable RX-operation
	SciaRegs.SCIFFRX.bit.RXFFINTCLR = 1;    // clear RX-FIFO INT Flag
	PieCtrlRegs.PIEACK.all = PIEACK_GROUP9;
}

I just checked the signal outputs from the device and the Peripheral Explorer. The device I am communicating with, has a normal High signal when it is idle, while the Peripheral Explorer has a low signal. I read that "The SCI uses a NRZ (Non-Return-to-Zero) format, which means that in an inactive state the SCIRX and SCITX lines will be held high.".

Why is the SCI output on my Peripheral Explorer held low? Is there a register that i must change?